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Varicella

Cause

The varicella zoster virus (VZV), a herpesvirus belonging to the subfamily
of Alphaherpesviridae.

Transmission

Transmission is via droplets, aerosol or direct contact, or indirectly
by touching freshly soiled contaminated items. Patients are usually
contagious from a few days before onset of the rash until the rash
has crusted over.

Nature of the disease

Varicella is an acute, highly contagious disease. In temperate climates
most cases occur before the age of 10 years. The epidemiology is less
well understood in tropical areas, where a relatively large proportion
of adults in some countries are seronegative. While mostly a mild
disorder in childhood, varicella tends to be more severe in adults. It is
characterized by an itchy, vesicular rash, usually starting on the scalp
and face, initially accompanied by fever and malaise. As the rash
gradually spreads to the trunk and extremities, the first vesicles dry
out. It normally takes about 7–10 days for all crusts to disappear. The
disease may be fatal, especially in neonates and immunocompromised
individuals. Complications include VZV-induced pneumonitis or
encephalitis and invasive group A streptococcal infections. Following
infection, the virus remains latent in neural ganglia; upon subsequent
reactivation, VZV may cause zoster (shingles), a disease affecting
mainly immunocompromised individuals and elderly people.

Geographical distribution

Worldwide.

Risk for travellers

Most adult travellers from temperate climates are immune to varicella
as a result of natural childhood disease or vaccination, whereas nonvaccinated
young individuals from areas of low varicella endemicity
may be at risk of infection when travelling to countries of high
endemicity. Immunocompromised individuals are at particular risk of
severe disease.